This invention relates to gear drives and particularly to an improved system for cooling a gear drive during operation.
The meshing gearing of a gear drive unit under load generates vast quantities of heat. Without some mechanism or system for removing the heat, the oil lubricant for the gearing may reach a temperature between 250 and 300 degrees F. At such temperature levels, the lubricant thins and oxidizes thereby destroying its ability to provide the necessary film between the contacting metal surfaces. Long exposure to high temperatures will also destroy the heat treatment of the gears and bearings, thereby reducing their hardness and leading to failures. A maximum oil bath temperature of 200 degrees F. is the design goal, and to achieve this it is necessary to provide a system for cooling the interior of the gear drive.
A variety of cooling systems have been proposed and used. A simple system mounts a fan on one or more of the shafts of the gearing to circulate air over the exterior of the gear drive housing. A more elaborate version splashes the oil bath against an impeller that mounts a fan external of the housing, with the impeller being surrounded by a series of hollow tubes that allow air to circulate through the housing under the influence of the fan. This later system is described in U.S. Pat. No. 4,414,861 issued Nov. 15, 1983 to Witt for "Gear Drive Cooling". Another approach is shown in U.S. Pat. No. 3,736,812 issued June 5, 1973 to Wellauer for "Speed Reducer Recirculating Cooling System". That system uses a fan to draw warm air from the interior of the housing, pass the air through a circulating water heat exchanger, and return the cooled air to the interior of the housing. Still another system inserts a bank of finned tubes into the top of the housing where they are exposed to the air and to lubricant that is splashed from the gearing. Cool water is circulated through the tubes to cool the air and the oil that is splashed against the tube.
All of the above systems cool the air in the drive housing, or the air and splashed oil, in an attempt to lower the operating temperature. The cooling system of this invention acts directly on the oil lubricant by exchanging heat between the oil and water circulating through heat exchangers that are submerged in the reservoir of oil in the base of the gear drive housing.